Nonwoven fabrics are used in absorbent articles, such as sanitary products and disposable diapers, cleaning products, such as wipers, and medical goods, such as masks. However, the nonwoven fabrics used in such products usually have functions suited for the particular purposes of the products and their location of use.
With absorbent articles, for example, it is necessary to employ nonwoven fabrics that expand and contract in response to bodily movement during wear or use, without creating an uncomfortable feeling for the user. Disposable diapers require nonwoven fabrics with high elasticity and strength sufficient to prevent tearing during extension, as well as satisfactory feel on the skin and air permeability.
The nonwoven fabrics having desired functions in such products are usually specially designed and produced for each product, and from the viewpoint of production cost and environmental protection, it is preferred for a nonwoven fabric having the desired performance to be one that can be easily produced by modification of a commercially available nonwoven fabric, for example.
As a method for producing a nonwoven fabric suitable for use in an absorbent article comprising a nonwoven fabric as the starting material, PTL 1 discloses a method for producing a nonwoven fabric with low stiffness and excellent flexibility, without collapse or dropping of the ridges and without obstruction of the open holes. Also, in paragraph ** of PTL 1 it is stated that a nonwoven fabric with bonded and entangled fibers may be used as the starting material for the nonwoven fabric.
However, when a commercially available nonwoven fabric, for example, is used as the starting material for the invention described in PTL 1, a high level of energy is required for fluid treatment because the fibers of the nonwoven fabric are fixed and not easily moved. When water vapor or an air stream is used as fluid treatment, the fluid treatment temperature must be increased, but a higher treatment temperature results in fusion of the fibers in the nonwoven fabric and reduced flexibility of the nonwoven fabric that is produced, while also making it difficult to form the desired structure. When a water stream is used as the fluid treatment, a drying step is also necessary.
According to the invention described in PTL 1, a carded web may be used as the starting material, but since using a carded web as the starting material tends to impair the texture of the produced sheet, it becomes necessary to increase the suction force during fluid treatment, resulting in larger production equipment.